Combustion synthesis/densification of an Al2O3-TiB2 composite

The self-propagating gasless combustion reaction 3TiO(2) + 3B(2)O(3) + 10Al --> 5Al(2)O(2) --> 3TiB(2) was used to produce an Al2O3-TiB2 composite, wh ich was densified by uniaxial loading immediately following completion of r eaction. The densification was enabled by the high temperatures produced by the combustion reaction( approximate to 2000 degreesC) which rendered the reaction product (approximate to 70% porosity) plastic. The microstructure was characterized by columnar TiB2 grains with a diameter of 1-2 mum and le ngth of 5-10 mum embedded in equiaxed Al2O3 (grain size approximate to 50 m um); the TiB2 phase tended to agglomerate in clusters. A few of the TiB2 gr ains exhibited dislocations, while the Al2O3 was annealed. This indicates t hat recovery processes took place after the plastic deformation involved in densification. Several constitutive models (corresponding both to rigid-pl astic and power-law creep material behavior) were used to describe the mech anical response of the porous and ductile ceramic product and compared to t he experimental results, with satisfactory agreement for power-law creep mo dels. These constitutive models have a temperature-dependent term that inco rporates the effect of specimen cooling, that occurs concurrently with dens ification; thus, it was possible to obtain a flow stress dependence of temp erature which is in reasonable agreement with values interpolated from lite rature experimental results. (C) 2001 Elsevier Science B.V. All rights rese rved.